It is proposed to record the vectorcardiogram (VCG) annually on a large group of men kept under continuous medical surveillance since 1953 in a prospective study of coronary heart disease and hypertension. The VCGs will be analyzed by a computer program developed by Pipberger and associates. Previous collaborative observations made with Pipberger on this same population suggest that in serial VCGs subtle changes may occur predictive of subsequent degenerative cardiovascular disease. This observation will be critically tested in a subset of men identified as being at particularly high risk of coronary heart disease by the multiple logistic function of Tryett, Cornfield and Kannel, in whom the VCG will be recorded every 3 months.